[llvm-objdump] Split disassembleObject and simplify --{start,stop}-address handling

The main disassembly loop is hard to read due to special handling of ARM
ELF data & ELF data. Split off the logic into two functions
dumpARMELFData and dumpELFData. Hoist some checks outside of the loop.

--start-address --stop-address have redundant checks and minor off-by-1
issues. Fix them.

llvm-svn: 357869